Experiments in this proposal are designed to determine the nature of the control of enzymatic interconversion of phylloquinone and phylloquinone-2,3- epoxide, reactions which require separate enzymes from liver microsomes. Techniques of protein purification, especially applied to the microsomal fraction of liver will be utilized in order to separate the components of each enzymatic reaction from each other and from extraneous and possibly interfering proteins. This will allow a more accurate study of the kinetics and inhibition of each enzyme and the mechanism of regulation of the interconversion of vitamin and epoxide. Other biologically active forms of vitamin K (e.g., menaquinone-9), non-coumarin inhibitors such as the structural analog 2- chloro-3-phytyl,4-naphthoquinone and tetrachloropyridinol as well as the inactive cis isomer of vitamin K will be examined in the epoxidase reaction to ascertain if biological activity is associated with substrate specificity of the enzyme. The postulated precursor protein of prothrombin will be used in these experiments to determine if the cyclic interconversion of vitamin K and the epoxide is coupled to the production of prothrombin.